There is well known an air conditioning:apparatus for an automotive vehicle, which comprises a compressor driven by an engine to compress an refrigerant, an evaporator for evaporating the refrigerant compressed by the compressor, and a blower fan for blowing introduced external air into a vehicle room through the evaporator. In an automotive vehicle on which the conventional air conditioning apparatus as described above is mounted, when the compressor is being actuated, the engine idle speed is increased by opening an AAC (auxiliary air control) valve by a constant opening rate. This AAC valve is usually disposed in an air passage bypassing a throttle valve, to adjust the flow rate of auxiliary air, for instance (as disclosed by NISSAN Service Weekly, June 1987, No. 578, B69 to 71 page).
In this specification, the status in which the compressor is being actuated implies a status in which the compressor is feeding the refrigerant, and the status in which the compressor is being not actuated implies a status in which the compressor is feeding almost no refrigerant. Accordingly in the case of a variable volume compressor, if the amount of refrigerant to be fed is zero in spite of the face that the compressor Is being actuated, the compressor is regarded as being not actuated.
In the automotive vehicle provided with the air conditioning apparatus as described above, even when the thermal load within the vehicle room is low, once the compressor is actuated, the engine idle speed is increased unconditionally. In the case where the thermal load is not high, however, since sufficient cooling performance can be usually obtained without increasing engine idle speed to increase the amount of refrigerant to be fed, there exists a problem in that an increase of the engine idle speed inevitably deteriorates the fuel consumption rate.